It is a randomized, double blind study, involving 80 children with ages from 1 to 10 years old, following eletive hypospadias surgery, under general anesthesia and caudal epidural block . The patients will be divided into 4 groups: bupivacaine alone, bupivacaine plus clonidine 1mcg/kg, bupivacaine plus clonidine 2 mcg/kg, bupivacaine plus clonidine 3 mg/kg. The peroperative consumption of anesthetics gases, heart rate and arterial blood pressure will be recorded. Postoperative pain will be evaluated by using FLACC scale ( faces , legs, activity , cry , consolability ) . Requiriments for supplementary postoperative analgesia at 24 h will be avaiable.